Our Milky Way galaxy contains a minimum of 100 billion planets, according to a detailed statistical study based on the detection of three planets located outside our solar system, called exoplanets. ...

... The survey results show that our galaxy contains, on average, a minimum of one planet for every star. This means that it's likely there is a minimum of 1,500 planets within just 50 light-years of Earth.

The study is based on observations taken over six years by the PLANET (Probing Lensing Anomalies NETwork) collaboration, using a technique called microlensing to survey the galaxy for planets. ...

As there are only 63 stars within 50 light years of earth, 1500 planets would mean some stars would have a lot of them.

Steve

Are we really sure about the low figure of 63?

Having not spent any time counting them myself, I am loathe to state anything as fact; but a quick search of previous counts and estimates from scientific sources places the 1500 figure on the conservative side. 1600 to over 2000 being the predominant range that I found.

As there are only 63 stars within 50 light years of earth, 1500 planets would mean some stars would have a lot of them.

Steve

Are we really sure about the low figure of 63?

Having not spent any time counting them myself, I am loathe to state anything as fact; but a quick search of previous counts and estimates from scientific sources places the 1500 figure on the conservative side. 1600 to over 2000 being the predominant range that I found.

The discrepancy is probably due to stating the number of Sun-Like stars which are Main sequence stars that are non binary. At one time I thought that there was a count of only 600 such stars out to 1000 light years

If a thought signal of extraterrestrial origin is supposed to be able to reach 300 light years out into space from its starting point, how many stars of type G, especially main sequence stars, would then lie within such a sphere?

Could the Drake equation be adjusted for specific types of stars within a given distance, or is the spectral class for a given star enough? Our sun is spectral class G2 V, in comparison.

Some stars getting old are evolving into subgiants and giants, changing their spectral types during this process and making possible existing life less likely near these objects. Procyon, having spectral class F5 IV-V is such an example.

An even more evolved star, Arcturus, is a Population 2 star. Its spectral class is K1.5IIIFe-0.5, according to http://en.wikipedia.org/wiki/Arcturus .

In between, we of course find Aldebaran (Alpha Tau) having a spectral class of K5III / M2V (meaning it has a red dwarf companion). This star I may guess is still a Population 1 star in comparison.

Stars like Sirius are main sequence stars of type A. A1 V to be exact when it comes to Sirius. They are hotter, bluer and more luminous than our own sun, but maybe not totally unsuitable for life forms given possible planets with atmospheres and liquid oceans orbiting such types of stars.

Also I came across the following web-page tonight: http://stars.astro.illinois.edu/sow/sowlist.html .

100 billion planets, that really is a massive number. You have to really think about that number to get your head around it.

How many of those planets have trees, and birds that fly in the Sky's, and flowing streams and rivers, and dinosaurs roaming freely across the plains. And great civilisations of people living out their lives.

I bet hundreds of thousands of them have life on them just like here on Earth.

While you have an interesting argument against intelligent life the shear numbers say that it's more likely than not. I'd hate to think that we are the only self aware beings in this galaxy let alone the universe
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In a rich man's house there is no place to spit but his face.
Diogenes Of Sinope

The number of planets with birds,dinosaurs or any other type of life we recognise on earth ,is definately a lot rarer than planets(which we
havent even discovered yet) that can contain even the most basic
forms of life.
Another planet with dinosaurs is theoretically probable,but almost certainly
non existant.

There may well be 100 billion lumps of rock orbiting distant stars, whether of not they can be classed as planets by our standards, is debatable. The odds are that there is likely to be intelligent life out there somewhere, but the odds are also very much against it being with two legs and two arms. Unless of course there is a race of self balancing intelligent chairs ....

In terms of space travel, the human race hasn't even started to crawl yet. Even in the 21st Century we couldn't send a simple craft to a space station in low earth orbit, without control rooms with dozens of scientists and tracking stations all over the world. And if it rains .... well, forget it.

I happen to think that ET is out there somewhere, and we are being kept an eye on by unmanned drones, which we call UFO's. But more than likely we are being ignored until we have the capability of FTL speed, or at least until we have spacecraft that have the ability to take off and land on their own.

While you have an interesting argument against intelligent life the shear numbers say that it's more likely than not. I'd hate to think that we are the only self aware beings in this galaxy let alone the universe

Because the amazing number of planets now possible: I am beginning to re-evaluate my thinking.
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A planet is a body that orbits the Sun, is massive enough for its own gravity to make it round, and has "cleared its neighbourhood" of smaller objects around its orbit. If we were to substitute "the sun" with "its star", I think we have a working definition of planet, surely?
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I think I am. Therefore I am. I think.

As there are only 63 stars within 50 light years of earth, 1500 planets would mean some stars would have a lot of them.

Steve

Are we really sure about the low figure of 63?

Having not spent any time counting them myself, I am loathe to state anything as fact; but a quick search of previous counts and estimates from scientific sources places the 1500 figure on the conservative side. 1600 to over 2000 being the predominant range that I found.

Hmm. I have three apples and four oranges. However there are seven pieces of fruit. If one were to re-define fruit as "non-citrus fruit", then my statement that I had seven fruits would be wrong by the new definition of fruit, but where would that leave apples? Are they no longer fruit?.

The original poster mentioned "stars". Not spectral type "G" stars. Of those there appears to be 64, granted. But the limit as to a specific spectral type was never given by the original poster.
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I think I am. Therefore I am. I think.

The point is that sheer numbers do not guarantee anything. The Drake equation ignores perhaps two dozen requirements for the evolution of intelligent life similar to ours (in terms of being able to compare with homo sapiens in it's current state of evolution.. These are things like temperature, stable orbits, non crushing gravity, a magnetic field, tides, a moon to tidally lock and stabilize spin, an outer gas giant to protect from excessive asteroid/comet hits. sufficient water, dry land, non-poisoness atmosphere, an ozone layer, etc. Perhaps not all of these are absolutely essential and there are probably a dozen more that I or others don't even know about.

if there were say only a dozen of these parameters and they were each only 20% likely then there would perhaps be a few hundred likely planets in our galaxy. On average they would be too far away to ever know if life existed. I think that there may be only a handful of such planets in our galaxy.

I could believe that life such as ours exists somewhere in the universe-I also believe that it is likely that we will never know.

The fact that recent searches may prove me wrong in my assumptions keeps me interested in the ongoing search.

If the numbers predicted by Frank Drake and others were valid the Galaxy would be colonized by now and we would be enjoying the chatter rather than listening to a bunch of thermal noise.

What I wonder is, will it make any difference in the long run. The possibility exists that travel back and forth between the stars will never be realized and therefore we may never make contact with our neighbors even assuming they are there.

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

What I wonder is, will it make any difference in the long run. The possibility exists that travel back and forth between the stars will never be realized and therefore we may never make contact with our neighbors even assuming they are there.

I agree. The distances are so great, excepting a breakthrough of light speed, travel will impossible.

But, this attempt is not really about communication between civilizations. It is, I believe, an attempt to see if there are other civilizations within our Galaxy.
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The point is that sheer numbers do not guarantee anything. The Drake equation ignores perhaps two dozen requirements for the evolution of intelligent life similar to ours...

The observations and numbers continue to reinforce the view that our solar system is nothing 'special'... The development of our form of life here might be peculiar and 'rare', but the circumstances are nothing special. Note also that life might be widespread in various forms...

I could believe that life such as ours exists somewhere in the universe-I also believe that it is likely that we will never know.

The fact that recent searches may prove me wrong in my assumptions keeps me interested in the ongoing search.

If the numbers predicted by Frank Drake and others were valid the Galaxy would be colonized by now and we would be enjoying the chatter rather than listening to a bunch of thermal noise.

We would have been visited long ago.

At the moment, we are playing a game of numbers and possibilities, That is what the Drake equation attempts to add up.

If there is already life in the universe that multiplies and travels, then to quote a famous phrase from Carl Sagan: "Where are they?"

The observation that we haven't seen anything yet, might suggest that we might be the first at least for our galaxy...

Keep searchin',
Martin
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